World powers negotiating with Tehran over its disputed nuclear programme must come up with new proposals before talks in Geneva on October 15 and 16, Iran's foreign minister said.

The United States wants Iran to respond to proposals made by world powers in February as a starting point for talks. If the parties cannot even agree on how to start the negotiations, it is less likely a resolution can be agreed within the six months in which Iranian President Hassan Rouhani says he wants a deal.

Britain, China, France, Russia and the United States - the five permanent members of the United Nations Security Council - plus Germany, the so-called P5+1, said in February they want Iran to stop enrichment of uranium to 20 per cent, ship out some stockpiles and shutter a facility where such enrichment is done.

In return, they offered relief on international sanctions on Iran's petrochemicals and trade in gold and other precious metals.

US officials said last week that Secretary of State John Kerry had secured agreement from his Chinese counterpart calling for Iran to respond positively to existing nuclear proposals by the six world powers.

"The previous P5+1 plan given to Iran belongs to history and they must enter talks with a new point of view," Foreign Minister Mohammad Javad Zarif said in an interview with Iranian state television late on Saturday.

"The players must put away this illusion that they can impose anything on the Iranian people."

The election of Rouhani in June and his appointment of US-educated Zarif as foreign minister and chief nuclear negotiator has raised hopes of a solution to the decade-old dispute over Iran's nuclear programme.

Western powers believe Iranian enrichment activities are a cover for achieving nuclear weapons capability, whereas Iran insists its programme is purely for civilian purposes - for generating electricity and for a medical research reactor.

Rouhani and Zarif both tried to dispel mistrust of the Islamic Republic with a series of meetings, speeches and media interviews around the UN General Assembly in New York at the end of last month which was capped with a phone call between the Iranian president and US President Barack Obama.

Both presidents face opposition at home from conservatives who fear their government may be too willing to grant concessions before the other side takes tangible steps.

Iran's Supreme Leader Ayatollah Ali Khamenei, the most powerful man in Iran and the person who has the final say on the nuclear issue, said on Saturday he supported Rouhani's diplomatic opening with the United States.

But he said some aspects of it were "not proper". Khamenei did not elaborate on his objections, but it was a possible reference to the phone conversation between Rouhani and Obama.

The supreme leader also said he did not trust the United States as a negotiating partner, a sentiment echoed by Zarif.

"Just as the supreme leader said, we do not trust them, and they must build the trust of the Iranian people towards them in public and private discussions," Zarif said. - Reuters